1. Field of the Invention
The present invention relates to a heat treatment apparatus for heating a semiconductor wafer or the like by irradiating a substrate thereof with heat rays.
2. Description of the Related Art
An irradiation type heat treatment apparatus is used for thermal diffusion treatment, thermal oxidation treatment, or annealing treatment of semiconductor wafers in the process of manufacturing semiconductor devices. This heat treatment includes a plurality of halide lamps in a process tube in order to directly emit light beams to the wafer. In the heat treatment of a single wafer, the temperature in the process tube including the wafer is detected with high precision in order to optimize the temperature of the heat treatment. In the conventional heat treatment apparatus, the temperature of the wafer is detected by a radiation thermometer.
However, since, in the conventional apparatus, heat rays from the wafer is influenced by the surface condition of the wafer, an error in the detected temperature results. The surface condition of the wafer varies according to types of thin films formed on the wafer. If heat rays from the wafer are detected, there occurs considerably greater irregularities and variety of the amounts and wavelengths of the detected heat rays. It is thus difficult to control the temperature of the wafer itself with high precision, and a difference occurs between a process temperature of one wafer and a process temperature of an other wafer, with the result that thermal treatment of the wafer cannot be performed uniformly.
Jpn. Pat. Appln. KOKAI Publication No. 61-129834 (Jpn. Pat. Appln. KOKOKU Publication No. 2-34164) discloses a heat treatment apparatus, which has halide lamps around a transparent process tube, for irradiating a wafer with heat rays through the wall of the process tube. This apparatus includes a heat ray absorption plate between the process tube and wafer. The heat ray absorption plate is made of quartz or another material having an infrared rays penetrable characteristic similar to that of quartz. It absorbs some of the heat rays (secondary heat rays having a long wavelength of 4 .mu.m or more) radiating from the wall of the process tube to thereby prevent the wafer from being overheated.
In the apparatus of the Japanese Publication, however, the temperature of the wafer cannot be controlled with high precision, even though the secondary heat rays radiating from the process tube to the wafer can be restricted by the heat ray absorption plate. Since, furthermore, the wafer is heated indirectly through the wall of the process tube and the heat ray absorption plate, a thermal response is slow, and the temperature of the entire wafer cannot be quickly increased or decreased to a target one.